#! perl -w
use strict;
require 5.008;
use threads;
use Thread::Queue;

# Adjust (slowly) till you find the optimum
use constant MAX_THREADS => 10;

my $dispatchQ = Thread::Queue->new();
my $resultsQ  = Thread::Queue->new();

sub worker {
	# While there's stuff to be done
	while( $dispatchQ->pending() ) {

		# Get the next serverb
		my $server = $dispatchQ->dequeue();

		# creat a new connection (A guess!!)
		my $smtp = Net::SMTP->new( $server );

		# do whatever is required
		my $result = 'Whatever';

		# Tack the server name on the front of the results
		# for later identification. The normal perl idiom of
		# using an (anonymous) array has the problem that it
		# causes rapid memory leaks. Using this simplistic
		# approach seems to be most reliable and scalable.

		$resultsQ->enqueue( join( $; , $server, $result ) );
	}
	return; # When there is nothing left to do, die.
}

# Create the pool
my @threads = map{ threads->create( \&worker ) } 1 .. MAX_THREADS;

# Read the list of servers
my @servers = do{ local (*ARGV, $/) = 'servers.list'; <> };

# Put the list on the queue
$dispatchQ->enqueue( @servers );

# While there is still work to be done
while( $dispatchQ->pending() ) {

	# Get the results as they become available
	my ($server, $result) = split $;, $resultsQ->dequeue();

    # Record the results somewhere.
}
# DispatchQ is empty, each thread will terminate once it completes its last task

$_->join for @threads; # Wait till they finish

# Record the last few results
while( my ($server, $result) = @{ $resultsQ->dequeue } ) {
    # Record the results somewhere.
}

__END__